Conventionally, the device shown in FIGS. 6 and 7 is known as a device or connector for connecting circuit boards to each other, which is used in order to connect a plurality of circuit boards to each other as disclosed in Japanese Patent Application No. 7-15107.
In FIGS. 6A and 6B, the device or connector 100 for connecting circuit boards to each other has a fastening shaft 101 used to fasten two circuit boards 109,110; a spacer member 104 is engaged around the fastening shaft 101 and maintains a gap between the two circuit boards 109,110; and an attachment screw 105 used to fasten both circuit boards 109,110 on shaft 101.
The fastening shaft 101 is a plastic body including a large-diameter section and a small-diameter section with a shoulder 102 at an intersection therebetween. The surface of the plastic body is nickel plated or coated with a conductive paint. A threaded fitting 103 with which the attachment screw 105 is engaged, is formed by insert molding in an upper portion of the small-diameter section of the fastening shaft 101. The spacer member 104 is a ring-shaped member of a plastic or metal material, and the circumference thereof is nickel plated.
Furthermore, an insertion hole 111, which is used for the insertion of the small-diameter section of the fastening shaft 110, is located in lower circuit board 109, and ground pads 113 are located on both an upper surface and a bottom surface of circuit board 109 around the periphery of insertion hole 111. A fastening hole 112 is located in the upper circuit board 110 into which the attachment screw 105 is inserted and the diameter of which is smaller than that of the fastening hole 112, and ground pads 114 are located on both an upper surface and lower surface of circuit board 110 around the periphery of fastening hole 112.
FIG. 7A to 7D illustrate the method by which circuit boards 109,110 are connected to each other using the device or connector 100, as shown in FIG. 6.
In order to connect the upper and lower circuit boards 110,109 to each other in an electrically-continuous state, the small-diameter section of the fastening shaft 101 is first inserted into the insertion hole 111 of the lower circuit board 109 so that the lower circuit board is carried on the shoulder 102 of the fastening shaft 101 as shown in FIG. 7A. Next, as shown in FIG. 7B, spacer member 104 is placed onto and press-fitted on the small-diameter section of fastening shaft 101, so that the lower circuit board 109 is clamped between the spacer member 104 and the shoulder 102 of the fastening shaft 101.
Then, as shown in FIG. 7C, the upper circuit board 110 is placed on the surface formed by an upper surface of the fastening shaft 101 and an upper surface of the spacer member 104; and, as shown in FIG. 7D, attachment screw 105 is screwed into the threaded fitting 103 via the fastening hole 112. As a result, the upper circuit board 110 and lower circuit board 109 are fastened together.
When the upper circuit board 110 and lower circuit board 109 are fastened together, the ground pads 113 and 114 of the respective circuit boards 109,110 are placed in a state of electrical continuity with each other via the attachment screw 105, spacer member 104 and fastening shaft 101.
In conventional device or connector 100 for connecting circuit boards to each other, the area used exclusively for the fastening of the circuit boards 109,110 is small, so that electronic devices can be made more compact. However, such interconnection requires two operations--an operation in which the insertion hole 111 of the lower circuit board 109 is placed onto the small-diameter section of the fastening shaft 101, and an operation in which the spacer member 104 is placed onto and press-fitted on the small-diameter section of the fastening shaft 101. Accordingly, the work required in order to connect the circuit boards 109, 110 is time consuming.
Furthermore, the fastening shaft 101 used for connection must be formed from a plastic body including a large-diameter section and a small-diameter section, and it is also necessary to insert-mold the threaded fitting 103 in the upper portion of the small-diameter section, and to apply a nickel plating or a conductive paint to the surface of the fastening shaft 101. In addition, it is necessary to apply a nickel plating to the periphery of the spacer member 104. As a result, the structure of the device is complicated, and the cost of manufacture is high.
Accordingly, the object of the present invention is to provide, at a low manufacturing cost, a device or connector for connecting circuit boards to each other in which the area used exclusively for fastening the circuit boards is small, the work required in order to connect the circuit boards to each other in an electrically-continuous state is simple, and the connector has a simple structure.